﻿// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
#if !NORANGE
namespace System;



#if NET45
using System.Runtime.CompilerServices;
#endif

/// <summary>Represent a range has start and end indexes.</summary>
/// <remarks>
/// Range is used by the C# compiler to support the range syntax.
/// <code>
/// int[] someArray = new int[5] { 1, 2, 3, 4, 5 };
/// int[] subArray1 = someArray[0..2]; // { 1, 2 }
/// int[] subArray2 = someArray[1..^0]; // { 2, 3, 4, 5 }
/// </code>
/// </remarks>
public readonly struct Range : IEquatable<Range>
{
    /// <summary>Represent the inclusive start index of the Range.</summary>
    public Index Start { get; }

    /// <summary>Represent the exclusive end index of the Range.</summary>
    public Index End { get; }

    /// <summary>Construct a Range object using the start and end indexes.</summary>
    /// <param name="start">Represent the inclusive start index of the range.</param>
    /// <param name="end">Represent the exclusive end index of the range.</param>
    public Range(Index start, Index end)
    {
        Start = start;
        End = end;
    }

    /// <summary>Indicates whether the current Range object is equal to another object of the same type.</summary>
    /// <param name="value">An object to compare with this object</param>
    public override bool Equals(object? value) =>
        value is Range r &&
        r.Start.Equals(Start) &&
        r.End.Equals(End);

    /// <summary>Indicates whether the current Range object is equal to another Range object.</summary>
    /// <param name="other">An object to compare with this object</param>
    public bool Equals(Range other) => other.Start.Equals(Start) && other.End.Equals(End);

    /// <summary>Returns the hash code for this instance.</summary>
    public override int GetHashCode()
    {
        return Start.GetHashCode() * 31 + End.GetHashCode();
    }

    /// <summary>Converts the value of the current Range object to its equivalent string representation.</summary>
    public override string ToString()
    {
        return Start + ".." + End;
    }

    /// <summary>Create a Range object starting from start index to the end of the collection.</summary>
    public static Range StartAt(Index start) => new(start, Index.End);

    /// <summary>Create a Range object starting from first element in the collection to the end Index.</summary>
    public static Range EndAt(Index end) => new(Index.Start, end);

    /// <summary>Create a Range object starting from first element to the end.</summary>
    public static Range All => new(Index.Start, Index.End);

    /// <summary>Calculate the start offset and length of range object using a collection length.</summary>
    /// <param name="length">The length of the collection that the range will be used with. length has to be a positive value.</param>
    /// <remarks>
    /// For performance reason, we don't validate the input length parameter against negative values.
    /// It is expected Range will be used with collections which always have non negative length/count.
    /// We validate the range is inside the length scope though.
    /// </remarks>
#if NET45
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
#endif
    // [CLSCompliant(false)]
    public (int Offset, int Length) GetOffsetAndLength(int length)
    {
        int start;
        Index startIndex = Start;
        if (startIndex.IsFromEnd)
            start = length - startIndex.Value;
        else
            start = startIndex.Value;

        int end;
        Index endIndex = End;
        if (endIndex.IsFromEnd)
            end = length - endIndex.Value;
        else
            end = endIndex.Value;

        if ((uint)end > (uint)length || (uint)start > (uint)end)
        {
            throw new ArgumentOutOfRangeException(nameof(length));
        }

        return (start, end - start);
    }
}

#endif